Stable triphenyl-methane dye leucos



United States Patent STABLE TRIPHENYL-METHANE DYE LEUCOS Sydney M. Spatz and Benjamin Lipka, Williamsville,

N.Y., assignors to Allied Chemical Corporation, New

York, N.Y., a corporation of New York No Drawing. Filed Aug. 26, 1963, Ser. No. 304,631 U.S. Cl. 260-391 5 Claims Int. Cl. C09b 11/00 This invention relates to novel derivatives of the triphenylmethane series. More particularly, it relates to substantially colorless leuco derivatives of triaminotriphenylmethanes which are stable on storage and particularly suited for use in pressure sensitive copy systems and to processes for the preparation of such derivatives.

It is known to produce colorations by the impact prin ing method wherein paper or an analogous base is coated with-a substantially colorless composition containing an electron donor material such as Crystal Violet Lactone, N-substituted derivatives of leucoaurarnines, e.g., N-bis (p-dimethylaminophenyl -n1ethylaniline, trisp-dimethylaminophenyl) methane leuco, andthe like, and the coating is placed in close contact with an acidic electron acceptor such as an acid clay such as attapulgite, kaolin, bentonite, or other acidic material such as zinc sulfide, calcium fluoride or organic acids such as succinic acid, tannic acid, citric acid, and the like, either on the same or a separate sheet of paper or similar base and the color developed in localized areas through pressure of a stylus or impact of a typewriter key. The chromogenic electron donor may be applied in the form of a wax emulsion in which the chromogen or mixture of two or more chromogens is dispersed in a wax coating vehicle. This composition is applied to the paper or similar support and the reverse side coated with the acidic electron acceptor substance. Several such double coated. papers are placed one upon the other so as to form a manifold system and thereby to obtain a series of copies upon color development by impact causing the intimate contact of the wax emulsions with the acidic acceptors in the localized areas of pressure. In addition to wax, other binders such as natural and synthetic resins are used.

It is known also to utilize a mixture of two electron donor substances, one such as a leucoauramine, which develops rapidly on contact with the acidic material, but which fades relatively rapidly, and the second, such as a triphenylrnethane leuco, which develops color more slowly on contact with acidic substances but which yields a more permanent coloration. The known systems of this type sufifer from the premature color development of the triphenylmethane leuco components which is believed to be due to the tendency of these components to migrate to the surface of the coatings, a characteristic which is believed to be related, at least in part, to the solubility characteristic of the leuco compound in the binder. For example, 2-chloro-Crystal Violet Luco, a particularly unstable substance in the wax system, is soluble in most waxes of the type used in such coating to the extent of about 1% or more. The replacement of one or more of the non-polar groups by polar groups in the chromogen molecule has the effect of reducing the wax solubility of the chromogen and also of substantially eliminating the tendency of premature color offset due to migration of the chromogen from the wax emulsion. However, these more insoluble derivatives are not stable on storage or when exposed to light for extended periods. Thus, stability has been a major problem, and the patent literature indicates that considerable efiort has been made to develop suitable methods for stabilizing the general class of triphenylmethane leucos of which the specific compounds set forth hereinafter are members.

3,429,900 Patented Feb. 25, 1969 Accordingly, an object of the present invention is to provide novel polyaminotriphenylmethane leucos which are stable on storage without requiring stabilizing additives.

Another object is to provide novel derivatives of triaminotriphenylmethane leucos which are substantially colorless, but which develop intense colorations on contact with an acidic material.

Stil another object of this invention is to provide substantially colorless leuco derivatives of triaminotriphenylmethanes which are of limited solubility in waxes and which are stable on storage and in daylight at ordinary temperatures.

Another object is to devise processes for the preparation of said novel polyaminotriphenylmethane leucos.

These and other objects and ancillary advantages of our invention will in part be obvious and in part appear in the following description.

The novel compounds of our invention are leuco derivatives of p0lyaminotriphenylmethane compounds of the following general formula:

wherein x is an integer, 2 or 3; R and R are each an alkyl group having no more than two carbon atoms; R is chlorine, bromine, methyl or ethyl; and R is hydrogen, dialkylamino or N hydroxyalkyl N alkyl amino wherein each alkyl radical contains no more than two carbon atoms, Preferably x is 2, R and R are each methyl, R is chlorine or methyl, and especially chlorine, and R is dimethylamino or diethylamino.

The compounds of our invention are characterized by superior stability in that they will not undergo premature color development for at least 72 hours in a carnauba wax coating on paper at a concentration of about 1 /2% (by weight) when exposed to light from a standard, Cool-White (G.E.) 40-watt fluorescent bulb positioned at a distance of 18 inches from the coated paper.

The novel compounds of our invention can be prepared by several methods, including those generally used for the synthesis of triarylmethane leuco bodies. In accordance with a preferred mode of preparation, a benzaldehyde compound containing a chloro, bromo, or lower alkyl substituent in the ortho position is condensed with about two mole equivalents of an (or a mixture of) N-alkanol- N-alkylaniline which is unsubstituted in the para position. The condensation is effected in the presence of an acidic catalyst.

As is evident, the reaction involves two moles of the aniline compound with one mole of the benzaldehyde compound. Preferably the aniline compound is used in slight excess in order to obtain optimum reaction. Larger excesses may be used but such use is usually unnecessary and in fact is not to be recommended, since these large excesses increase the difficulty of isolating the desired product of the reaction.

The following ortho substituted benzaldehydes exemplify the class of compounds which can be used in this procedure:

2-bromobenzaldehyde 2-chloro benzaldehyde 3 o-Tolualdehyde 2-bromo-4-dimethylaminobenzaldehyde 2-chloro-4-dimethylaminobenzaldehyde 2-chloro-4-N-ethyl-N-methylaminobenzaldehyde 2-bromo-4-N-Bhydroxethyl-N-methylbenzaldehyde 4-diethylarnino-o-tolualdehyde 4-N-B-hydroxyethyl-N-methyl-o-tolualdehyde As representatives of the class of N alkanol N-alkylanilines which can be used in the process of our invention, the following compounds are mentioned:

2- (N-methylanilino) ethanol 2- (N-ethylanilino) ethanol 2- (-N-ethylanilino) propanol-l 2- (N-methylanilino propanol-l Strong, Water-soluble, non-oxidizing acids such as sulfuric acid, phosphoric acid, hydrochloric acid, formic acid, trichloroacetic acid, p-toluene sulfonic acid and the like are suitable acidic catalysts for carrying out the condensations. Because of its ready availability and reasonable cost, sulfuric acid is preferred. The quantity of this acid catalyst is not critical, but preferably should not be less than about two mol equivalents of acid per mol of benzaldehyde compound used. Larger quantities can be used, but may be objectionable since such larger quantities will consume correspondingly larger quantities of alkali in the neutralization step. Lesser quantities of the acidic catalyst may result in slower reaction velocities and even incomplete condensation and hence, may be disadvantageous from this viewpoint.

The rate of the reaction and the yield obtained can be further improved by carrying out the condensation in the presence of urea or a related compound. Preferably at least about 0.5 mol of this compound which functions as a catalyst, is used per mol of aldehyde. In addition to urea, thiourea, nitrourea, biuret, biurea, and various substituted urea and thiourea compounds may be used.

A solvent for the aldehyde and aniline is preferably present during the condensation. As organic solvent, any of the usual alcoholic solvents, such as methanol, ethanol, isopropanol, or the lower alkyl ethers of ethylene glycol or the like, or mixtures of two or more of such solvents may be used. The amount of such solvents used is not critical and may vary over a considerable range. Sufiicient solvent should be used to obtain a readily stirrable reaction mixture, but not so much as to result in excessive heat requirement to obtain a refluxing reaction temperature.

The temperature used in the condensation of our invention may vary over broad limits. Preferably, it should be above 50 C. and especially within the range of 70 to 90 C. A temperature within this range is conveniently obtained by the use of isopropanol as the solvent and maintaining the reaction mixture boiling under reflux conditions. Higher temperatures can be used, but are unnecessary and in fact undesirable since such would involve the use of relatively costly pressure apparatus or of higher boiling solvents which are costly and difiicult to recover. Temperatures below 50 C. are not recommended since the reaction rate becomes progressively slower and the time required to obtain acceptable conversions becomes inordinately long.

To recover the product the reaction mass may be cooled and the acid catalyst neutrailized by the addition of alkali, e.g., sodium hydroxide. The neutral to slightly alkaline solution is filtered to removed inorganic salts and/or other insoluble materials and the clarified filtrate after dilution with water to incipient crystallization is permitted to stand in a cool place to allow the leuco product to crystallize from solution.

It was indeed surprising to discover that leuco polyaminotriphenylmethane compounds containing a chlorine, bromine, methyl or ethyl radical as the substituent R in the above formula were stable on storage or exposure to light for extended periods without the need for stabilizing additives and that such compounds were eminently suitable as slow developing chromogens for impact printing compositions. Thus, wax emulsions containing N,N'- (B-hydroxyethyl)-N,N-diethyl N,N' dimethyl-4,4'- 4"-triaminotriphenylmethane leuco when coated on paper produced color prematurely on exposure to ordinary daylight for several days. However, a similar wax emulsion containing 2"-chloro N,N',N",N"-tetramethyl-N,N'-bis (B-hydroxyethyl)-4,4,4"-triaminotriphenylmethane leuco when coated on paper was practically free of color on exposure, under similar conditions, to ordinary daylight for several weeks. The discovery described herein gains added significance in view of the fact that the previously mentioned patent literature discloses, in listing the reactants suitable for producing triphenylmethane leucos, certain of the specific compounds employed in the herein described process, and yet this same literature then goes on to call for the addition of a stabilizer.

The wax used to prepare the emulsions described herein may be any of those commonly used by those skilled in the art of pressure sensitive copy systems such as, carnauba Wax and montan wax. In addition, natural and synthetic resin binders can be used e.g., polyvinyl alcohol, cellulose acetate Pliolite and others.

The invention will be illustrated by the following examples in which parts are by weight and temperatures are given in degrees centigrade. It will be understood that the invention is not limited to the specific details set out therein since, as will be obvious to those skilled in this art, changes can be made Without departing from the scope or spirit of our invention.

EXAMPLE 1 A mixture of 37.9 parts of 2-chloro-4-N,N-dimethyl aminobenzaldehyde, 59 parts of Z-(N-methylanilino) ethanol, 29.5 parts of 100% sulfuric acid, 18 parts of urea and about 200 parts of isopropanol is heated to boiling and maintained thereat under reflux conditions for two hours. After the dilution of the reaction mass with parts of water, the mixture is cooled to ambient temperature. The mixture is rendered slightly alkaline to Brilliant Yellow by the addition of 30% aqueous sodium hydroxide and the precipitate of sodium sulfate which forms is separated by filtration. The filter cake is washed with 50% aqueous isopropanol, directing the wash liquor into the clarified filtrate. The mixture is then diluted with Water until it is just hazy and the haze is cleared up :by the addition of just enough isopropanol. The resulting solution is permitted to stand in a cool place for about 16 hours. The resulting crystal slurry is agitated in insure complete crystallization and then it is filtered.

The product, 2-chloro-N', "-bis-B-hydroxyethyl-N,N, N, "-tetramethyl-4,4',4"-triaminotriphenylmethane leuco, corresponding to the formula HO 0112032 CHaCHzOH H O H CH;

CH3 CHz and melting at 142 to 144, is a light buff colored solid. The crystalline product is stable for several weeks against color development on exposure to air. Also, when 1.5 parts of this compound was mixed with 98.5 parts of a wax emulsion the resulting composition was used to coat paper, practically no color had developed on the coated paper after several weeks exposure to ordinary daylight. The corresponding product prepared by substituting an equivalent amount of 4-N,N-dimethylaminobenzaldehyde in the above procedure is relatively unstable in air, developing considerable color after several days exposure to air.

EXAMPLE 2 A mixture of 38.2 parts of 4-N,Ndiethylarnino-o-tolualdehyde, 57.8 parts of Z-(N-methylanilino) ethanol, 29.4 parts of 100% sulfuric acid, 12.8 parts of urea, and about 166 parts of isopropanol is heated at the boiling point of the mixture under reflux for two hours. After the addition of 90 parts water, the mixture is cooled to ambient temperature. The mass is rendered slightly alkaline to Brilliant Yellow by the addition of 30% aqueous sodium hydroxide. The precipitate of sodium sulfate is separated by filtration and the precipitate is washed with 50% aqueous isopropanol. The wash liquor is combined with the clarified filtrate and diluted with water to incipient oiling. The haziness is cleared up with just enough isopropanol and the clear solution permitted to stand for about 16 hours. The resultant crystal slurry is filtered to yield after drying about 34 parts of a light bufl colored solid melting at 122 to 125. This product is 2-methyl-N,N-diethyl- N,N"-dimethyl-N',N bis(B-hydroxyethyl)-4,4',4"-triaminotriphenylmethane leuco, corresponding to the formula This product is stable against color development on exposure to air for a period of several weeks. It is but slightly less stable in this respect than the analogous 2-chloro compound and substantially more so than the analogous 2-H derivative.

EXAMPLE 3 The procedure of Example 1 above is repeated except that in place of 2-chloro-4,N,N-dimethylaminobenzaldehyde, a molecularly equivalent amount of 2-chlorobenza1- dehyde is used. Pale buff crystals of 2-chloro-N,N"-bis (B-hydroxyethyl)-N,N"-dimethyl-4',4"-diaminotriphenylmethane leuco corresponding to the formula HOCHaCHa CHzCHzOH N- N CH; g1 CH3 are obtained which are stable against color development on exposure to air and ordinary light for several weeks.

It can thus be seen that a novel class of polyaminotriphenylmethane leuco compounds characterized by excellent stability against color development on exposure to air and hence of excellent storage stability have been devised. These compounds because of their polar nature are poorly soluble in wax compositions intended for use as paper coatings in the manufacture of impact printing manifold copy systems. Such compositions contained dispersed therein a compound of this invention provide manifold copy papers of excellent stability against premature color development and hence, are highly useful and desirable.

x is an integer selected from the group consisting of 2 and 3,

R and R are each alkyl groups having no more than two carbon atoms,

R is selected from the group consisting of chlorine,

bromine, methyl and ethyl, and

R is dialkylamino, wherein the alkyl radical contains no more than two carbon atoms.

2. The compound described in claim 1 wherein x is two, R and R are each methyl and R is chlorine.

3. Compound of claim 1 wherein x is 2, R R and R are methyl and R is dimethylamino.

4. As a stable leuco dye, 2 chloro N,N"-bis-B- hydroxyethyl N,N,N',N"-tetramethyl-4,4', "-triaminotriphenyl-methane leuco.

5. As a stable leuco dye, 2-methylN,N-diethyl-N,N"- dimethyl N,N"-bis(B-hydroxyethyl) 4,4,4" triaminotriphenyl-methane.

References Cited UNITED STATES PATENTS 2,726,252 12/ 1955 Balon et al 260391 2,755,203 7/1956 Stallman 260393 FOREIGN PATENTS 13,604 11/1914 Great Britain.

LORRAINE A. WEINBERGER, Primary Examiner.

H. C. WEGNER, Assistant Examiner.

US. Cl. X.R. 10623; 260-393 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,429,900 February 25, 1969 Sydney M. Spatz et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 9, "Stil" should read Still line 38, "atoms, should read atoms. Column 4, line 49, "in" should read to Column 6, line 14, "derivings" should read derivatives ---7 lines 43 and 44, 2methyl-N,N

diethyl-N,Ndimethyl-N ,N-bis (B-hydroxyethyl) 4 ,4 ,4"triaminotriphenyl-methane should read 2-methyl-N,Ndiethyl-N' ,N"dimethyl-N ,N"bis(B-hydroxyethyl)4,

4 ,4" ,triaminotriphenyl-methane Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. STABLE LEUCO DERIVINGS OF POLYAMINOTRIPHENYLMETHANE HAVING THE FORMULA 